What Is a Scanning Electron Microscope? A scanning electron microscope (SEM) uses electrons instead of light to form images. Since their development in the early 1950s, SEMs have developed new areas of study in the medical and physical science communities. The advantages of an SEM are that it has a large depth of field, which allows more of a specimen to be in focus at one time, and it also has much higher resolution, so closely spaced specimens can be magnified at much higher levels. Because the SEM uses electromagnets rather than lenses, researchers have much more control over the degree of magnification. The disadvantages of SEMs are that they are expensive, large, and must be housed in an area free of any possible electric, magnetic, or vibration interference. They are also limited to solid, inorganic samples small enough to fit inside the vacuum chamber that can handle moderate vacuum pressure. oped a human-robot collaborative system where the robot follows the motion of a torch operated by a human welder,” Zhang explained. “In this case, the motion of the human welder is not planned in advance. We use a sensor to track the torch’s motion and command the robot to follow the motion in real time.” The robot Zhang’s group uses is a UR 5 from Universal Robots USA, Inc., East Setauket, N.Y. He prefers this robot because most industrial robots do not allow their motion to be changed in real time, but Universal Robots do. “Using this human-robot collaborative system, we can allow the robot to carry sensors to see the welding process. The measurement from the sensors can be displayed to the human welder and the human welder can adjust the welding parameters per the display. The adjustment will be realized by the robot. As such, the human welder will not carry sensors such that he can operate freely to adjust the welding speed and torch orientation per the feedback of the welding process. We will be able to record what the welder sees and how the torch responds to that to analyze how the welder operates,” Zhang explained. LeTourneau University The lab at LeTourneau University, Longview, Tex., contains a variety of specialized equipment such as a microwave welding machine, shortcircuit detector, high-speed cameras, and infrared cameras. However, the school’s modified DSI Gleeble® 1500 thermal-mechanical simulator plays an important role in much of the work as does varestraint testing equipment. Professor Yoni Adonyi holds the Omer Blodgett Chair of Welding & Materials Joining Engineering at Le- Tourneau and is also Materials Joining Engineering Program Coordinator. According to Adonyi, “The main focus of our research has always been simulating welding and other manufacturing processes by ‘deconstructing’ the thermal and mechanical processes involved using the Gleeble. After collecting real data from welding processes, we feed them into the Gleeble software and simulate different processes by ‘reconstructing’ them, using different heat inputs, etc., without making any welds.” They focus their energies on finding mechanical, physical, and other properties under dynamic conditions such as high heating and cooling rates, or strain rates. Adonyi desribes physical simulations as the “missing link” between numerical simulations and real life. To illustrate what he means, he said, “Most computer models are inaccurate because they use static or not timedependent material properties from handbooks (for example, slowly heating samples to high temperatures and then measuring their strength by slowly pulling on them). In reality, in welding and forging processes, heating rates of hundreds of degrees per second and strain rates of many feet/second occur and properties change dramatically. “To illustrate this difference, a steel heated to 1000°F can elongate like chewing gum when slowly pulled, reaching almost 100% elongation and no strength. On the other hand, if pulled at 3 ft/s, the same steel breaks like glass with no elongation or close to 0% and considerable strength. The Gleeble is able to produce these dynamic properties, and if we feed those results into computer models, they become more accurate.” In the case of the LeTourneau group, they did compressive loading and measured the deformation rates at different temperatures, then fed the data into a high-frequency (forge) weld model. Similarly, they found changes in the Curie temperature (the temperature at which ferromagnetic materials lose their magnetic properties on heating vs. cooling) as a function of heating rates. Recently, a U.S. patent was issued to Adonyi, Baylor University Prof. Seung Kim, and former students Ithamar Glumac and Allen Worcester for a closed-loop controlled standing-wave, 3-kW microwave welding machine. This type of research equipment was not available commercially, so the Le- Tourneau group designed and fabricated one. Breakthroughs. Dynamic recrystallization conditions for high-frequency weld optimization, plus dissimilar sold-liquid interface simulations for centrifugal casting and weld cladding. Wish list. A Gleeble® 3500. Canadian Centre for Welding and Joining The Canadian Centre for Welding and Joining (CCWJ), associated with the Dept. of Chemical and Materials Engineering at the University of Alberta, Edmonton, is “located right at the epicenter of manufacturing for the oil sands operations, and is the central point for weld-related issues in the oil sands,” related Prof. Patricio Mendez, the center’s director, and Program Manager Dr. Goetz Dapp. “The CCWJ holds a preeminent place in Canada in carrying out welding research in direct interaction and collaboration with the industry,” Dapp said. The center functions “as a liaison between the industry, equipment manufacturers, consumable manufacturers, and the global research community, and plays a key role in introducing technological advances and new technologies to the industry to drive innovation, increase productivity, and optimizing process and procedures. We offer the unique ability to combine fundamental research with practical, industry-related and industry-driven applications, and with our excellent connections in the international welding and research communities ensure that the industry can 52 WELDING JOURNAL / JULY 2016
Welding Journal | July 2016
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